The present invention relates to a traction/compression buffer for coupling devices on rail and wheel-mounted vehicles, comprising a housing and a piston element, which projects out of said housing on one side and which can be moved out of a zero position in two directions against the resistance of a spring device and a damping device.
Double-acting traction/compression buffers of the type indicated above dampen collision impacts acting in the direction of pressure as well as tractive impacts acting in the direction of traction; in particular, they are used in a variety of vehicles, namely in rail-mounted vehicles. There a heavily damped compression and a weakly damped rebound movement of the piston element upon collision impacts and a weakly damped withdrawal and a strongly damped return movement of the piston element upon tractive impacts is sought. In a known generic traction/compression buffer the housing has a cavity in which is inserted a buffer cartridge that combines a spring devicexe2x80x94acting to return the piston element from its compressed position and a damping devicexe2x80x94damping reentry of the piston element into the housingxe2x80x94and is acted on by the piston element upon the shove into the housing triggered by collision impacts. For cushioning tractive impacts, by which the piston element is drawn out of the housing, metallic spring rings sliding in axial direction to one another are provided in a ring-shaped cavity formed between the piston element and the housing, while the damping characteristic of particularly the return movement of the piston element into the zero position is defined by the friction between individual spring rings.
The high weight of this known generic traction/compression buffer in particular is disadvantageous. In addition, the known traction/compression buffers are relatively costly.
The object of the present invention, which consists in procuring a traction/compression buffer of the generic type that is distinguished from the prior art by lower weight as well as by lower manufacturing costs, derives from the problems described above.
According to the present invention, this object is accomplished in that for damping the return movement of the piston element out of the position in which it is drawn out of the housing in the direction of the zero position, there is provided a hydraulic damping device which comprises a ring-shaped hydraulic working chamber that surrounds the piston element and is connected to an overflow chamber by at least one overflow channel. In other words, the traction/compression buffer according to the invention is characterized in that a damping device acting hydraulically is provided for damping the return movement of the piston element in the case of tractive impacts. Said hydraulic damping device comprises essentially a ring-shaped hydraulic working chamber, which inside is limited by the piston element and outside preferably by the housing. The volume of this ring-shaped hydraulic working chamber is reduced when the piston element is drawn out of the housing beyond its zero position. Then a damping medium is forced out of the ring-shaped hydraulic working chamber through the at least one overflow channel into an overflow chamber. Upon return of the piston element out of its drawn-out position in the direction of the zero position, caused by the spring device acted on in response to the tractive impact, the damping medium flows out of the overflow chamber through thexe2x80x94preferably narrowedxe2x80x94overflow channels back into the ring-shaped hydraulic working chamber, owing to which the return movement is damped.
The design of the traction/compression buffer according to the invention thus allows the damping device damping the return movement of the piston element upon tractive impacts to be integrated or accommodated in that housing that also accommodates the damping device damping the compression movement of the piston element upon collision impacts. Consequently, efficient traction/compression buffers can be made especially compact and with small dimensions. This immediately results in a weight reduction, as well as in a reduction of manufacturing costs. In addition, for certain applications it is of advantage that, owing to the compact design of the traction/compression buffer according to the invention, the space required for its installation may turn out to be relatively small.
A first preferred refinement of the traction/compression buffer according to the invention is characterized in that the piston element is designed as a cylindrical hollow piston surrounding a cavity, the overflow chamber within the cylindrical cavity being divided by a separating piston guided sealingly displaceable therein. Accommodation of the overflow chamber in the interior of the piston element in turn is of special advantage with regard to compact design of the traction/compression buffer. There the separating piston within the cylindrical cavity surrounded by the hollow piston is deflected according to the overflow volume of the damping medium out of the ring-shaped hydraulic working chamber into the overflow chamber. This may be utilized in connection with another preferred refinement, in that the cylindrical cavity surrounded by the hollow piston is divided by the separating piston into the overflow chamber on one side and a spring chamber on the other side. Accordingly, in this refinement the spring device absorbing tractive impacts is accommodated in the cylindrical cavity surrounded by the hollow piston; it acts on that face of the separating piston that stands opposite the face turned toward the overflow chamber. Basically, a variety of configurations are possible for the structural design of the spring device. Thus, for example, mechanical springs such as bolts and disk springs may be used, as well as elastomer blocks or alternatively gas- pressure springs. Of special advantage, again with regard to the weight as well as to the compactness of the traction/compression buffer according to the invention, is design of the spring device in the form of a gas-pressure spring.
Another preferred refinement of the traction/compression buffer according to the invention is characterized in that the ring-shaped hydraulic working chamber is closed axially by an annular piston that is guided sealingly displaceable on the inner surface of the housing and on the outer surface of the piston element. This form of axial closure of the ring-shaped hydraulic working chamber makes it possible for its volume to be altered only upon withdrawal of the piston element from the housing beyond the zero position, but not upon insertion of the piston element in the housing beyond the zero position. In this way, the damping device acting to dampen the return movement of the piston element upon tractive impacts in no way influences the damping behavior of the damping device damping collision impacts. If, upon collision impacts, the piston element is pushed out of its zero position into the housing, the annular piston follows the movement of the piston element, so that the volume of the ring-shaped hydraulic working chamber does not change. There the annular piston especially preferably is caused to follow by a driver provided on the outer surface of the piston element, which in the zero position of the piston element lies on the face of the annular piston.
According to an alternative, the annular piston may be converted into a cylinder sleeve in which the head part of the piston element is guided sealingly displaceable. In this case the ring-shaped hydraulic working chamber is not limited on the outside by the housing, but rather by the cylinder sleeve connected to the annular piston.
Particularly preferably, a hydraulic damping device is also provided for damping press-in of the piston element into the housing upon collision impacts. According to a preferred refinement of the invention, said damping device comprises a hydraulic high-pressure chamber limited by the piston element, the housing and an intermediate wall, said chamber being connected to a low-pressure chamber by at least one overflow channel. There the housing may in particular comprise a cylindrical cavity that is divided by a separating piston, guided sealingly displaceable, into a spring chamber in which is accommodated the spring device producing return of the pressed-in piston element into its zero position, and the hydraulic low-pressure chamber. Then the at least one overflow channel connecting the high-pressure chamber with the low-pressure chamber is provided in the intermediate wall of the housing. This refinement of the traction/compression buffer according to the invention again permits it to be built especially compactly and easily, and thus to be produced at a low cost.
An especially advantageous refinement is characterized in that the overflow channel is assigned a control element that influences the flow cross section and is connected to the piston element. The position of the control element with respect to the at least one overflow channel thus varies depending upon the position of the piston element relative to the housing. In this way the damping characteristic of the damping device damping collision impacts can be selectively adjusted as a function of the extent to which the piston element moves into the housing, in order to make the damping force as constant as possible over the entire stroke path. Then the control element may in particular be designed as a control pin projecting relatively far into the overflow channel and whose cross section varies in the axial direction. Alternatively to this, the control element may be designed in the form, for example, of a control sleeve having bores that are increasingly closed upon entry of the control sleeve into the overflow channel.
If the housing, in the manner described above, has an intermediate wall delimiting the hydraulic high-pressure chamber, according to another preferred refinement of the invention there is provided at least one overload channel that connects the high-pressure chamber with the low-pressure chamber and to which is assigned an overpressure valve. Such an overload system, comprising an overload channel and a pressure-relief valve, acts to reduce pressure selectively in the high-pressure chamber at extreme conditions, in order to prevent damage to the traction/compression buffer. At the same time, the overload safety system provides an especially compact and light-weight design of the traction/compression buffer according to the invention.
Lastly, according to a refinement of the invention it may be provided that the at least one overflow channel of the hydraulic damping device damping the return movement of the piston element from its position drawn out of the housing into the zero position is assigned a throttle valve acting on one side. The latter reduces the flow cross section of the at least one overflow channel, upon the return flow of the damping medium out of the overflow chamber into the ring-shaped hydraulic working chamber, upon rebound of the piston element out of its drawn-out position into its zero position. Incidentally, when a suitable throttle valve acting on one side is used, the flow cross section of the at least one flow channel can be selected great enough so that the withdrawal movement of the piston element out of the housing, in which the throttle valve is not active, takes place alone, practically undamped, against the force of the corresponding spring device.